Gen-art review of draft-ietf-sip-media-security-requirements-07

I have been selected as the General Area Review Team (Gen-ART)
reviewer for this draft (for background on Gen-ART, please see
_http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html_).

Please resolve these comments along with any other Last Call comments
you may receive.

Document: draft-ietf-sip-media-security-requirements-07.txt
Reviewer: Elwyn Davies
Review Date:  10 October 2008
IETF LC End Date: 13 October 2008
IESG Telechat date: (if known) -

Summary:
This document is almost ready for the IESG.  I have a couple of comments
and queries about the reasoning in a few of the requirements.
Meta-comment:  To a non-SIPper the problems to be solved and the
requirements look very challenging!  And to think S in SIP might once
have meant...
Disclaimer: Whilst the requirements appear sensible and internally
consistent, I have no idea if the set is complete or really appropriate.
The explanations in s4 are very helpful and clear for a naive reader
like me. Likewise, I do not have the necessary knowledge to verify the
statements in the various appendices relating to existing proposals.
Again they look reasonable sensible.

Comments:
s5.1, Requirement R-RTP-VALID:  I think some explanation of  why '...the key
         negotiation packets MUST NOT pass the RTP validity check
         defined in Appendix A.1 of [RFC3550].' would help.  This looks